Inter vivos tubes, such as endotracheal tubes, are used to provide gases to the lungs during surgery. The endotracheal tube is inserted into the trachea with its distal tip advanced halfway toward the tracheal bifurcation to provide gases, such as oxygen and anesthetics. The exposed portion of the endotracheal tube is then firmly taped to the patent's face to prevent undesirable movement.
To align the position of the prior art endotracheal tube, the inflatable cuff balloon, at the distal end of the endotracheal tube, is inflated to correspond to the inner diameter of a portion of the trachea, thereby centering or otherwise positioning the endotracheal tube within the trachea. The cuff balloon, however, does not completely obstruct the entire trachea, only the portion where it is anchored. When the cuff balloon is inflated, confirmation of the tube's contact within the trachea is achieved, and delivery of anesthetic gases is performed.
Because of various sized endotracheal tubes, it is preferable to at least make the outer diameter of the endotracheal tube to be closely proximate to the size of the glottis, or opening between the vocal cords, for selective positioning of the endotracheal tube at a predetermined location. Therefore, various sized tubes are used, and the anesthesiologist or nurse anesthetist must choose from a variety of sized tubes to insert.
Present day endotracheal tubes vary in size and are numbered according to internal diameter (ID). For example, for children, tubes are measured of about 3.5-7 mm internal diameter, and from 7-11 mm for an adult.
The internal diameter in women varies in general from 7.0 to 8.5 mm ID and in men from 8 to 10 mm ID. Therefore, the endotracheal tube size selected for each patient is empirically selected by the anesthesiologist based on the patent's gender, age and size.
Ideally, the endotracheal tube should approximate as closely as possible the glottic size of the patient. Since there is no way to estimate the glottic size prior to the administration of anesthesia, in the existing prior art endotracheal tubes, a distal inflatable cuff is incorporated into the present day endotracheal tube which, when inflated, compresses the tracheal wall, thus creating a closed circuit between the endotracheal tube inflow from the anesthesia machine and outflow from the patent's lung to the exhalation valve.
Furthermore, as noted in "Clinical Anesthesia", 1989 Edition, J. B. Lippincott Company, edited by Paul Barash, MD, Bruce Cullen, MD, and Robert Stoelting, MD, it is stated:
"Endotracheal tube resistance varies inversely with the tube size. Each millimeter decrease in tube size is associated with an increase in resistance of 25-100%. The work of breathing parallels changes in resistance. A 1 mm decrease in tube size increases the work of breathing 34-154%, depending on the ventilatory pattern".
Therefore, in existing prior art tubes, the internal diameter is small, and the only large portion is the external cuff balloon. This makes it harder for a surgical patient to breathe through the small internal diameter of the existing endotracheal tubes.
Applicant's prior U.S. Pat. Nos. 3,968,800 dated Jul. 13, 1976 and 4,827,925 dated May 9, 1989 describe an adjustable endotracheal tube which is complex to expand, and which does not have flexibility in being adapted to varying sized tracheas of different patients. Applicant's other prior U.S. Pat. No. 4,722,335 dated Feb. 2, 1988 discloses an expandable endotracheal tube including two overlapping curved segments, which when joined together form a closed tube. However, the configuration may be conceptually possible but in practical terms, difficult to construct and maintain at present prices.